Measurements of lung interstitial to plasma albumin concentration ratios in vitro in this laboratory have consistently shown values of one (1.0) in normal dogs, rabbits, man, and monkeys. It is suggested that in vivo convective exchanges of water in excess of ablumin across the capillary leads to an equilibrium of Starling's forces. This hypothesis will be tested, first, by examining regional differences of the ratio in vertical lungs (this hypothesis predicts no differences) and, second, by causing graded hydrostatic edema when a decreased ratio is predicted. Distribution of albumin and water, both intra and extracellularly, is markedly altered during mechanical ventilation. A study in dogs designed to localize the sites of water and albumin accumulation is planned during long-term ventilatory support. Techniques for assessment of organ water and protein will continue development and comparative studies of lung composition in health and edema will be undertaken. Assessment of capillary permeability by radioisotope equilibration and by multiple indicator dilution analysis is planned with emphasis on in vivo techniques appropriate for use in patients. A current trend clinically is to ignore plasma oncotic replacement during resuscitation. It is suggested that in the presence of pulmonary change, a reduced plasma oncotic pressure represents a reduced reserve against pulmonary edema and, hence, pulmonary impairment may be enhanced. This will be tested in a rabbit model.